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      SUBROUTINE <a name="CHPEVD.1"></a><a href="chpevd.f.html#CHPEVD.1">CHPEVD</a>( JOBZ, UPLO, N, AP, W, Z, LDZ, WORK, LWORK,
     $                   RWORK, LRWORK, IWORK, LIWORK, INFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  -- LAPACK driver routine (version 3.1) --
</span><span class="comment">*</span><span class="comment">     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
</span><span class="comment">*</span><span class="comment">     November 2006
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Scalar Arguments ..
</span>      CHARACTER          JOBZ, UPLO
      INTEGER            INFO, LDZ, LIWORK, LRWORK, LWORK, N
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      INTEGER            IWORK( * )
      REAL               RWORK( * ), W( * )
      COMPLEX            AP( * ), WORK( * ), Z( LDZ, * )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Purpose
</span><span class="comment">*</span><span class="comment">  =======
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  <a name="CHPEVD.21"></a><a href="chpevd.f.html#CHPEVD.1">CHPEVD</a> computes all the eigenvalues and, optionally, eigenvectors of
</span><span class="comment">*</span><span class="comment">  a complex Hermitian matrix A in packed storage.  If eigenvectors are
</span><span class="comment">*</span><span class="comment">  desired, it uses a divide and conquer algorithm.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  The divide and conquer algorithm makes very mild assumptions about
</span><span class="comment">*</span><span class="comment">  floating point arithmetic. It will work on machines with a guard
</span><span class="comment">*</span><span class="comment">  digit in add/subtract, or on those binary machines without guard
</span><span class="comment">*</span><span class="comment">  digits which subtract like the Cray X-MP, Cray Y-MP, Cray C-90, or
</span><span class="comment">*</span><span class="comment">  Cray-2. It could conceivably fail on hexadecimal or decimal machines
</span><span class="comment">*</span><span class="comment">  without guard digits, but we know of none.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Arguments
</span><span class="comment">*</span><span class="comment">  =========
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  JOBZ    (input) CHARACTER*1
</span><span class="comment">*</span><span class="comment">          = 'N':  Compute eigenvalues only;
</span><span class="comment">*</span><span class="comment">          = 'V':  Compute eigenvalues and eigenvectors.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  UPLO    (input) CHARACTER*1
</span><span class="comment">*</span><span class="comment">          = 'U':  Upper triangle of A is stored;
</span><span class="comment">*</span><span class="comment">          = 'L':  Lower triangle of A is stored.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  N       (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The order of the matrix A.  N &gt;= 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  AP      (input/output) COMPLEX array, dimension (N*(N+1)/2)
</span><span class="comment">*</span><span class="comment">          On entry, the upper or lower triangle of the Hermitian matrix
</span><span class="comment">*</span><span class="comment">          A, packed columnwise in a linear array.  The j-th column of A
</span><span class="comment">*</span><span class="comment">          is stored in the array AP as follows:
</span><span class="comment">*</span><span class="comment">          if UPLO = 'U', AP(i + (j-1)*j/2) = A(i,j) for 1&lt;=i&lt;=j;
</span><span class="comment">*</span><span class="comment">          if UPLO = 'L', AP(i + (j-1)*(2*n-j)/2) = A(i,j) for j&lt;=i&lt;=n.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">          On exit, AP is overwritten by values generated during the
</span><span class="comment">*</span><span class="comment">          reduction to tridiagonal form.  If UPLO = 'U', the diagonal
</span><span class="comment">*</span><span class="comment">          and first superdiagonal of the tridiagonal matrix T overwrite
</span><span class="comment">*</span><span class="comment">          the corresponding elements of A, and if UPLO = 'L', the
</span><span class="comment">*</span><span class="comment">          diagonal and first subdiagonal of T overwrite the
</span><span class="comment">*</span><span class="comment">          corresponding elements of A.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  W       (output) REAL array, dimension (N)
</span><span class="comment">*</span><span class="comment">          If INFO = 0, the eigenvalues in ascending order.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Z       (output) COMPLEX array, dimension (LDZ, N)
</span><span class="comment">*</span><span class="comment">          If JOBZ = 'V', then if INFO = 0, Z contains the orthonormal
</span><span class="comment">*</span><span class="comment">          eigenvectors of the matrix A, with the i-th column of Z
</span><span class="comment">*</span><span class="comment">          holding the eigenvector associated with W(i).
</span><span class="comment">*</span><span class="comment">          If JOBZ = 'N', then Z is not referenced.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LDZ     (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The leading dimension of the array Z.  LDZ &gt;= 1, and if
</span><span class="comment">*</span><span class="comment">          JOBZ = 'V', LDZ &gt;= max(1,N).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  WORK    (workspace/output) COMPLEX array, dimension (MAX(1,LWORK))
</span><span class="comment">*</span><span class="comment">          On exit, if INFO = 0, WORK(1) returns the required LWORK.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LWORK   (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The dimension of array WORK.
</span><span class="comment">*</span><span class="comment">          If N &lt;= 1,               LWORK must be at least 1.
</span><span class="comment">*</span><span class="comment">          If JOBZ = 'N' and N &gt; 1, LWORK must be at least N.
</span><span class="comment">*</span><span class="comment">          If JOBZ = 'V' and N &gt; 1, LWORK must be at least 2*N.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">          If LWORK = -1, then a workspace query is assumed; the routine
</span><span class="comment">*</span><span class="comment">          only calculates the required sizes of the WORK, RWORK and
</span><span class="comment">*</span><span class="comment">          IWORK arrays, returns these values as the first entries of
</span><span class="comment">*</span><span class="comment">          the WORK, RWORK and IWORK arrays, and no error message
</span><span class="comment">*</span><span class="comment">          related to LWORK or LRWORK or LIWORK is issued by <a name="XERBLA.86"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  RWORK   (workspace/output) REAL array, dimension (MAX(1,LRWORK))
</span><span class="comment">*</span><span class="comment">          On exit, if INFO = 0, RWORK(1) returns the required LRWORK.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LRWORK  (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The dimension of array RWORK.
</span><span class="comment">*</span><span class="comment">          If N &lt;= 1,               LRWORK must be at least 1.
</span><span class="comment">*</span><span class="comment">          If JOBZ = 'N' and N &gt; 1, LRWORK must be at least N.
</span><span class="comment">*</span><span class="comment">          If JOBZ = 'V' and N &gt; 1, LRWORK must be at least
</span><span class="comment">*</span><span class="comment">                    1 + 5*N + 2*N**2.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">          If LRWORK = -1, then a workspace query is assumed; the
</span><span class="comment">*</span><span class="comment">          routine only calculates the required sizes of the WORK, RWORK
</span><span class="comment">*</span><span class="comment">          and IWORK arrays, returns these values as the first entries
</span><span class="comment">*</span><span class="comment">          of the WORK, RWORK and IWORK arrays, and no error message
</span><span class="comment">*</span><span class="comment">          related to LWORK or LRWORK or LIWORK is issued by <a name="XERBLA.102"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  IWORK   (workspace/output) INTEGER array, dimension (MAX(1,LIWORK))
</span><span class="comment">*</span><span class="comment">          On exit, if INFO = 0, IWORK(1) returns the required LIWORK.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LIWORK  (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The dimension of array IWORK.
</span><span class="comment">*</span><span class="comment">          If JOBZ  = 'N' or N &lt;= 1, LIWORK must be at least 1.
</span><span class="comment">*</span><span class="comment">          If JOBZ  = 'V' and N &gt; 1, LIWORK must be at least 3 + 5*N.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">          If LIWORK = -1, then a workspace query is assumed; the
</span><span class="comment">*</span><span class="comment">          routine only calculates the required sizes of the WORK, RWORK
</span><span class="comment">*</span><span class="comment">          and IWORK arrays, returns these values as the first entries
</span><span class="comment">*</span><span class="comment">          of the WORK, RWORK and IWORK arrays, and no error message
</span><span class="comment">*</span><span class="comment">          related to LWORK or LRWORK or LIWORK is issued by <a name="XERBLA.116"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INFO    (output) INTEGER
</span><span class="comment">*</span><span class="comment">          = 0:  successful exit
</span><span class="comment">*</span><span class="comment">          &lt; 0:  if INFO = -i, the i-th argument had an illegal value.
</span><span class="comment">*</span><span class="comment">          &gt; 0:  if INFO = i, the algorithm failed to converge; i
</span><span class="comment">*</span><span class="comment">                off-diagonal elements of an intermediate tridiagonal
</span><span class="comment">*</span><span class="comment">                form did not converge to zero.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  =====================================================================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Parameters ..
</span>      REAL               ZERO, ONE
      PARAMETER          ( ZERO = 0.0E+0, ONE = 1.0E+0 )
      COMPLEX            CONE
      PARAMETER          ( CONE = ( 1.0E+0, 0.0E+0 ) )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      LOGICAL            LQUERY, WANTZ
      INTEGER            IINFO, IMAX, INDE, INDRWK, INDTAU, INDWRK,
     $                   ISCALE, LIWMIN, LLRWK, LLWRK, LRWMIN, LWMIN
      REAL               ANRM, BIGNUM, EPS, RMAX, RMIN, SAFMIN, SIGMA,
     $                   SMLNUM
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Functions ..
</span>      LOGICAL            <a name="LSAME.141"></a><a href="lsame.f.html#LSAME.1">LSAME</a>
      REAL               <a name="CLANHP.142"></a><a href="clanhp.f.html#CLANHP.1">CLANHP</a>, <a name="SLAMCH.142"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>
      EXTERNAL           <a name="LSAME.143"></a><a href="lsame.f.html#LSAME.1">LSAME</a>, <a name="CLANHP.143"></a><a href="clanhp.f.html#CLANHP.1">CLANHP</a>, <a name="SLAMCH.143"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           <a name="CHPTRD.146"></a><a href="chptrd.f.html#CHPTRD.1">CHPTRD</a>, CSSCAL, <a name="CSTEDC.146"></a><a href="cstedc.f.html#CSTEDC.1">CSTEDC</a>, <a name="CUPMTR.146"></a><a href="cupmtr.f.html#CUPMTR.1">CUPMTR</a>, SSCAL, <a name="SSTERF.146"></a><a href="ssterf.f.html#SSTERF.1">SSTERF</a>,
     $                   <a name="XERBLA.147"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC          SQRT
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Test the input parameters.
</span><span class="comment">*</span><span class="comment">
</span>      WANTZ = <a name="LSAME.156"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( JOBZ, <span class="string">'V'</span> )
      LQUERY = ( LWORK.EQ.-1 .OR. LRWORK.EQ.-1 .OR. LIWORK.EQ.-1 )
<span class="comment">*</span><span class="comment">
</span>      INFO = 0
      IF( .NOT.( WANTZ .OR. <a name="LSAME.160"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( JOBZ, <span class="string">'N'</span> ) ) ) THEN
         INFO = -1
      ELSE IF( .NOT.( <a name="LSAME.162"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'L'</span> ) .OR. <a name="LSAME.162"></a><a href="lsame.f.html#LSAME.1">LSAME</a>( UPLO, <span class="string">'U'</span> ) ) )
     $          THEN
         INFO = -2
      ELSE IF( N.LT.0 ) THEN
         INFO = -3
      ELSE IF( LDZ.LT.1 .OR. ( WANTZ .AND. LDZ.LT.N ) ) THEN
         INFO = -7
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.EQ.0 ) THEN
         IF( N.LE.1 ) THEN
            LWMIN = 1
            LIWMIN = 1
            LRWMIN = 1
         ELSE
            IF( WANTZ ) THEN
               LWMIN = 2*N
               LRWMIN = 1 + 5*N + 2*N**2
               LIWMIN = 3 + 5*N
            ELSE
               LWMIN = N
               LRWMIN = N
               LIWMIN = 1
            END IF
         END IF
         WORK( 1 ) = LWMIN
         RWORK( 1 ) = LRWMIN
         IWORK( 1 ) = LIWMIN
<span class="comment">*</span><span class="comment">
</span>         IF( LWORK.LT.LWMIN .AND. .NOT.LQUERY ) THEN
            INFO = -9
         ELSE IF( LRWORK.LT.LRWMIN .AND. .NOT.LQUERY ) THEN
            INFO = -11
         ELSE IF( LIWORK.LT.LIWMIN .AND. .NOT.LQUERY ) THEN
            INFO = -13
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.201"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="CHPEVD.201"></a><a href="chpevd.f.html#CHPEVD.1">CHPEVD</a>'</span>, -INFO )
         RETURN 
      ELSE IF( LQUERY ) THEN
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Quick return if possible
</span><span class="comment">*</span><span class="comment">
</span>      IF( N.EQ.0 )
     $   RETURN
<span class="comment">*</span><span class="comment">
</span>      IF( N.EQ.1 ) THEN
         W( 1 ) = AP( 1 )
         IF( WANTZ )
     $      Z( 1, 1 ) = CONE
         RETURN 
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Get machine constants.
</span><span class="comment">*</span><span class="comment">
</span>      SAFMIN = <a name="SLAMCH.221"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>( <span class="string">'Safe minimum'</span> )
      EPS = <a name="SLAMCH.222"></a><a href="slamch.f.html#SLAMCH.1">SLAMCH</a>( <span class="string">'Precision'</span> )
      SMLNUM = SAFMIN / EPS
      BIGNUM = ONE / SMLNUM
      RMIN = SQRT( SMLNUM )
      RMAX = SQRT( BIGNUM )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Scale matrix to allowable range, if necessary.
</span><span class="comment">*</span><span class="comment">
</span>      ANRM = <a name="CLANHP.230"></a><a href="clanhp.f.html#CLANHP.1">CLANHP</a>( <span class="string">'M'</span>, UPLO, N, AP, RWORK )
      ISCALE = 0
      IF( ANRM.GT.ZERO .AND. ANRM.LT.RMIN ) THEN
         ISCALE = 1
         SIGMA = RMIN / ANRM
      ELSE IF( ANRM.GT.RMAX ) THEN
         ISCALE = 1
         SIGMA = RMAX / ANRM
      END IF
      IF( ISCALE.EQ.1 ) THEN
         CALL CSSCAL( ( N*( N+1 ) ) / 2, SIGMA, AP, 1 )
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Call <a name="CHPTRD.243"></a><a href="chptrd.f.html#CHPTRD.1">CHPTRD</a> to reduce Hermitian packed matrix to tridiagonal form.
</span><span class="comment">*</span><span class="comment">
</span>      INDE = 1
      INDTAU = 1
      INDRWK = INDE + N
      INDWRK = INDTAU + N
      LLWRK = LWORK - INDWRK + 1
      LLRWK = LRWORK - INDRWK + 1
      CALL <a name="CHPTRD.251"></a><a href="chptrd.f.html#CHPTRD.1">CHPTRD</a>( UPLO, N, AP, W, RWORK( INDE ), WORK( INDTAU ),
     $             IINFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     For eigenvalues only, call <a name="SSTERF.254"></a><a href="ssterf.f.html#SSTERF.1">SSTERF</a>.  For eigenvectors, first call
</span><span class="comment">*</span><span class="comment">     <a name="CUPGTR.255"></a><a href="cupgtr.f.html#CUPGTR.1">CUPGTR</a> to generate the orthogonal matrix, then call <a name="CSTEDC.255"></a><a href="cstedc.f.html#CSTEDC.1">CSTEDC</a>.
</span><span class="comment">*</span><span class="comment">
</span>      IF( .NOT.WANTZ ) THEN
         CALL <a name="SSTERF.258"></a><a href="ssterf.f.html#SSTERF.1">SSTERF</a>( N, W, RWORK( INDE ), INFO )
      ELSE
         CALL <a name="CSTEDC.260"></a><a href="cstedc.f.html#CSTEDC.1">CSTEDC</a>( <span class="string">'I'</span>, N, W, RWORK( INDE ), Z, LDZ, WORK( INDWRK ),
     $                LLWRK, RWORK( INDRWK ), LLRWK, IWORK, LIWORK,
     $                INFO )
         CALL <a name="CUPMTR.263"></a><a href="cupmtr.f.html#CUPMTR.1">CUPMTR</a>( <span class="string">'L'</span>, UPLO, <span class="string">'N'</span>, N, N, AP, WORK( INDTAU ), Z, LDZ,
     $                WORK( INDWRK ), IINFO )
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     If matrix was scaled, then rescale eigenvalues appropriately.
</span><span class="comment">*</span><span class="comment">
</span>      IF( ISCALE.EQ.1 ) THEN
         IF( INFO.EQ.0 ) THEN
            IMAX = N
         ELSE
            IMAX = INFO - 1
         END IF
         CALL SSCAL( IMAX, ONE / SIGMA, W, 1 )
      END IF
<span class="comment">*</span><span class="comment">
</span>      WORK( 1 ) = LWMIN
      RWORK( 1 ) = LRWMIN
      IWORK( 1 ) = LIWMIN
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="CHPEVD.283"></a><a href="chpevd.f.html#CHPEVD.1">CHPEVD</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

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